1. Field of the Invention
This invention relates to a resonant wave filter consisting of a plurality of cascade-coupled resonators of the type commonly used in microwave communication equipment and, more particularly, to a resonant wave filter which can be made compact in size without loss of performance.
2. Prior Art Statement
As a resonant wave filter of the aforesaid type for use in microwave communication equipment, there has up to now been exclusively used the coaxial dielectric resonant wave filter. As shown in FIG. 8(a), for enhanced compactness, this conventional resonant wave filter is constituted of quarter-wave coaxial resonators 1a, 1b, 1c having respective central conductors 2a, 2b, 2c and filled with dielectric material. As illustrated, the quarter-wave resonators 1a, 1b, 1c are, for example, arranged in parallel and sequentially capacity coupled. Where particularly sharp band filter characteristics are required, there has been used the waveguide dielectric resonator. In this resonator, square waveguide dielectric resonators 4a, 4b, 4c exhibiting high Q value are cascade-coupled via partitions 16, 17 as shown for example in FIG. 8(b).
While the coaxial dielectric resonator of FIG. 8(a) is compact, it cannot achieve a high Q value and thus is incapable of providing sufficiently sharp band filter characteristics. Moreover, since it employs capacitive coupling, it is structurally complex.
On the other hand, since in the waveguide dielectric resonant wave filter of FIG. 8(b) input/output coupling is achieved by inserting probes 14, 15 into the waveguide dielectric resonators 4a, 4c, these endmost resonators fail to provide the desired high Q value in spite of being large in size.